Research methods and Comparative examination of pinniped craniofacial musculature and its role in aquatic feeding

• Main Author: Kienle, Sarah
• Format: Other/Unknown Material
• Language: unknown
• Published: Zenodo 2022
• Subjects: Mirounga angustirostris; Northern elephant seal; Zalophus californianus; California sea lion; Weddell seal; Leptonychotes weddellii; Pusa hispida; ringed seal; Phoca vitulina; harbor seal; Erignathus barbatus; Bearded seal; Craniofacial muscles; Musculoskeletal; mastication; Biting; Suction; Suction feeding; hyoid; facial morphology; Facial muscles; tongue; feeding; bearded seal; Elephant Seal; Elephant Seals; Weddell Seal; Weddell Seals; walrus*
• Online Access: https://doi.org/10.5281/zenodo.6585360

Secondarily aquatic tetrapods have many unique morphological adaptations for life underwater compared to their terrestrial counterparts. A key innovation during the land-to-water transition was feeding. Pinnipeds, a clade of air-breathing marine carnivorans that includes seals, sea lions, and walruses, have evolved multiple strategies for aquatic feeding (e.g., biting, suction feeding). Numerous studies have examined pinniped skull and dental specializations for underwater feeding. However, data on the pinniped craniofacial musculoskeletal system and its role in aquatic feeding are rare. Therefore, the objectives of this study were to conduct a comparative analysis of pinniped craniofacial musculature and examine the function of the craniofacial musculature in facilitating different aquatic feeding strategies. We performed anatomical dissections of 35 specimens across six pinniped species. We describe 32 pinniped craniofacial muscles—including facial expression, mastication, tongue, hyoid, and soft palate muscles. Pinnipeds broadly conform to mammalian patterns of craniofacial muscle morphology. Pinnipeds also exhibit unique musculoskeletal morphologies—in muscle position, attachments, and size—that likely represent adaptations for different aquatic feeding strategies. Suction feeding specialists (bearded and northern elephant seals) have a significantly larger masseter than biters. Further, northern elephant seals have large and unique tongue and hyoid muscle morphologies compared with other pinniped species. These morphological changes likely help generate and withstand suction pressures necessary for drawing water and prey into the mouth. In contrast, biting taxa (California sea lions, harbor, ringed, and Weddell seals) do not exhibit consistent craniofacial musculoskeletal adaptations that differentiate them from suction feeders. Generally, we discover that all pinnipeds have well-developed and robust craniofacial musculature. Pinniped head musculature plays an important role in facilitating different ...